1. Field of the Invention
This invention relates to input devices for use in display computer terminals.
2. Description of the Prior Art
The "joystick", the "tracker ball" and the Stanford Research Institute "mouse" are typical analog devices used for cursor positioning purposes with digital computer display terminals. These devices, which are described on pages 171 through 174 of Principles of Interactive Computer Graphics by W. M. Newman and R. F. Sproull (McGraw-Hill, 1973), typically include potentiometers. To obtain more accurate cursor positioning with such devices, the resolution of any portion of their potentiometers may be temporarily increased by using either of the circuits disclosed in applicant's application Ser. No. 939,266, filed on even date herewith. In particular, when a conventional potentiometer is combined with either of these circuits the output voltage vs. rotation characteristic is parabolic in nature where the parabolic relationship starts anew from the point where rotation of the potentiometer is reversed to provide very high resolution immediately following the reversal. This permits any voltage level within the range available to the potentiometer to be precisely selected, thus improving cursor positioning.
Since digital computers operate in discrete steps, it is frequently necessary to convert the above-described analog voltage into a digital format before it can be utilized. In some instance it may be preferable to produce cursor positioning information directly in a digital format while having a vernier type of action similar to that described above.